In various apparatuses using a superconductive material for a main portion, when a conventional metal superconductive wire is used, the wire must be cooled to a liquid helium temperature close to absolute zero. In such apparatuses, since a margin between a use environment temperature and a critical temperature at which superconductivity of the superconductive wire is lost is small, cooling is performed by immersion cooling or forced circulating cooling of liquid helium.
On the contrary, in recent years, a high-temperature superconductive wire which can be put into a superconducting state with liquid nitrogen having the absolute temperature of 77k have been developed. Such a superconductive wire can stably obtain a superconductive condition through conduction cooling of the superconductor by an ultra-low temperature refrigerator.
FIG. 1 shows an example of a superconduction apparatus using such a superconductive wire. The superconduction apparatus 101 includes a vacuum adiabatic vessel (cryostat) 102. The inside of the vacuum adiabatic vessel 102 is put into a vacuum state by evacuation through an exhaust port 108. A superconducting coil 103 is arranged within the vacuum adiabatic vessel 102. The superconducting coil 103 is cooled by a superconducting coil cooling refrigerator 105. An internal surface of the vacuum adiabatic vessel 102 is covered with a radiation shield. The radiation shield is cooled by a radiation shield cooling refrigerator 106. The superconducting coil 103 is electrically connected to an external electrical apparatus through a current lead 104. An internal state of the vacuum adiabatic vessel 102 is monitored by a measuring unit arranged at a measurement port 107. The high-temperature superconductive wire material can be cooled by such a unit.
In the superconduction apparatus, the superconductor is also used for a current lead for supplying power to a main part as well as for the main part which performs a basic function of the device. The ultra-low temperature refrigerator is used to cool the superconductor and remove heat entered from the outside.
FIG. 2 shows an example of the current lead of the superconduction apparatus. The vacuum adiabatic vessel 110 is hermetically sealed by fixing a lid 114 with an opening flange 115. The vacuum adiabatic vessel 110 includes a manhole 113. An internal surface of the vacuum adiabatic vessel 110 is covered with a radiation heat shield member 112. The inside of the vacuum adiabatic vessel 110 is put into a vacuum state by evacuation through an evacuating and dry gas injecting port 127. An internal superconductor 111 is arranged within the vacuum adiabatic vessel 110. The internal superconductor 111 is connected to a cold head 117 of an internal superconductor cooling apparatus 116 through a cooling conductor 118. The internal superconductor cooling apparatus 116 is an ultra-low temperature refrigerator for cooling the internal superconductor 111 to a temperature for keeping the internal superconductor 111 in the superconducting state.
A conductor of the internal superconductor 111 is further connected to one end of a superconduction current lead 123 through a conductor 124. The other end of the superconduction current lead 123 is connected to a normal conduction current lead 121. A cooling conductor 122 cools a connection between the superconduction current lead 123 and the normal conduction current lead 121. The other end of the normal conduction current lead 121 is connected to a conductor 120 outside of the vessel 110. An end of the conductor 120 is used as an external power supply system interface. The internal superconductor 111 is electrically connected to an external electrical apparatus through the conductor 124, the superconduction current lead 123, the normal conduction current lead 121 and the conductor 120. The cooling conductor 122 is connected to a cold head 126 of a current lead cooling unit 125. The current lead cooling unit 125 cools the superconduction current lead 123 through the cooling conductor 122 so as to put the lead 123 into the superconduction state.
In such a superconduction apparatus, the cold head 117 of the internal superconductor cooling apparatus 116, the internal superconductor 111, the cold head 126 of the current lead cooling unit 125 and the cooling conductor 118 are accommodated in the common vacuum adiabatic vessel 110. In building and maintenance of the refrigerator and the current lead, in a state which the temperatures of the superconductor and the cooling conductor are increased, a person enters the inside of the vessel from the manhole 113 and performs connecting and disconnecting operations. An assembly of the superconductor and the refrigerator is previously assembled and installed in the vacuum adiabatic vessel 110 through the opening flange by opening it.
In order to improve a low-temperature strength and reduce gas generation which causes lowering of the degree of vacuum, a vacuum shield vessel in such superconduction apparatus has a welded assembly structure made of stainless steel. Mounting seats for external units such as a refrigerator and a current lead, an opening flange and a mounting seat for the manhole are airtightly sealed with an O-ring or the like.
The ultra-low temperature refrigerator can cool a front cooling head portion to ultra low temperature through adiabatic expansion of helium gas. The cooling conductor 118 is made of material such as copper, which is easy to conduct heat and electricity.
An evacuating and dry gas injecting port 127 is also used to introduce dry air or dry nitrogen gas into the vacuum adiabatic vessel 110 for breaking for breaking the vacuum state and raising the internal temperature while preventing dew formation. After completion of the operation, the following evacuation is performed and then initial cooling is performed from a room temperature state to an ultra-low temperature state over a long time.
The superconduction apparatus shown in FIGS. 1 and 2 have following problems.
(1) In the operation of connecting an ultra-low temperature refrigerator, an internal superconductor and a current lead, an operator needs to enter into the vacuum adiabatic vessel and performs complicated operations in a narrow closed space, which is inefficient. In addition, the entire inside of the apparatus needs to be opened, which is also inefficient.
(2) In order to secure a space for accommodating the ultra-low temperature refrigerator and the current leads in the vacuum adiabatic vessel for the internal superconductor, it is needed to increase the size of the vessel. Since these units are dispersively arranged, useless spaces are generated.
(3) In a maintenance operation such as inspection and exchange of the ultra-low temperature refrigerator and the current lead, it takes a long time to break the vacuum state of the vacuum adiabatic vessel, raise the temperature of the internal superconductor and initial cooling of the superconductor and the cooling conductor after completion of the above-mentioned operation. Accordingly, it is need to stop the apparatus for a long time, leading to a large economic loss.
(4) A working space needs to be secured in the vacuum adiabatic vessel which accommodates the internal superconductor therein. For this reason, there are the constraints of a shortest cooling path from the ultra-low temperature refrigerator to the superconductor and the number of installed ultra-low temperature refrigerators.
In conjunction with the above description, a superconducting magnet apparatus is described in Japanese Patent Publication JP 2006-324325A (the first conventional example), in which the magnet apparatus is accommodated in a vacuum adiabatic vessel and includes a superconducting coil dipped in liquid helium or having a conduction cooling structure without use of liquid helium. In the magnet apparatus, a current lead for leading a current from an external power supply to the superconducting coil includes a room-temperature side current lead of copper or copper alloy, a middle current lead of high-temperature superconductor, and a low-temperature side current lead of high-temperature superconductor which are connected in series. The middle current lead and the low-temperature side current lead are arranged in a adiabatic vacuum region, and a connection between the middle current lead and the low-temperature side current lead is cooled by a small-size refrigerator, without passing cooling gas or liquid through the insides of these current leads.
Also, a vacuum vessel for nuclear fusion is described in Japanese Patent Publication JP-a-Heisei 10-104376 (the second conventional example), in which the vacuum vessel confines plasma and is divided into sectors in a torus direction, and a dross receiver is provided outside the sector along the division plane.
Also, a division type tubular magnetic shield apparatus is described in Japanese Patent Publication JP 2004-179550A (the third example), in which the magnetic shield apparatus has a plurality of C-shaped shaking blocks which are combined to form a magnetic shield space in the inside and each of which has a C-shaped lateral cross section and a predetermined length in an axial line direction. The C-shaped shaking block includes a magnetic material layer having an angular magnetization characteristic and a coil wound at least a part of an inner layer or an outer layer of the magnetic material layer to supply magnetic shaking current to the C-shaped shaking block.
Also, a nuclear fusion apparatus is described in Japanese Patent No. 2,633,876 (the fourth conventional example), in which the nuclear fusion apparatus includes a vacuum vessel of a hollow annular shape, a plurality of superconducting toroidal magnetic field coils, and a vacuum adiabatic vessel. The vacuum vessel is supported to a base and plasma is confined therein. The plurality of coils surround the vacuum vessel and are arranged in a torus circumferential direction in a predetermined interval, and are supported to the base by adiabatic supporting columns. The vacuum adiabatic vessel accommodates the coils and the vacuum vessel. Each of the superconducting toroidal magnetic field coil and the vacuum vessel is supported movably in a horizontal direction by three or more oscillation preventing support units arranged on the torus circumference in an equal interval. Each of the support units includes movable attaching sections, a fixed attaching section and connecting members. The movable attaching sections are provided for each of outer circumference sections of the coil and the vacuum vessel in an equal pitch. The fixed attaching section is provided for the adiabatic vacuum vessel on a line in a torus tangent direction perpendicular to a line between the movable attaching section and a torus center. The connecting member connects the movable attaching section and the fixed attaching section. A set of the movable attaching section and the connecting member, or a set of the fixed attaching section and the connecting member are rotatably coupled by a pin.